1. Field of the Invention
The present invention relates to a method of battery economising in a communications system, a communications system, a transmitting station for use in the system and to a receiving station for use in the system. The communications system may comprise a telecommunications system such as a paging or cordless/cellular telephone system or telemetry system used for example in say an automatic meter reading system.
2. Description of the Related Art
In many telecommunications and telemetry applications, equipments are on standby for extended periods of times, for example months if not years. Consequently for battery powered equipments, any means of extending the useful life of a battery power source is of importance. For radio equipments the receiver is often the dominant source of power consumption within the equipment.
Power saving in receivers of radio equipments is known for example in the digital paging field. For example the POCSAG (or CCIR Radiopaging Code No. 1) has an inherent power saving capability because under the protocol time is divided into successive time periods called batches. A batch comprises a sync code word and 8 frames. A receiver is powered for receipt of a sync code word and for a predesignated one of eight frames in successive batches, any messages for the receiver being transmitted in the predesignated frame. During the time periods between the sync code word and the predesignated frame and vice versa, the receiver can be powered down.
EP-B1-0 554 941 discloses the option of a paging system controller transmitting address or receiver identity codes (RICs) in an order of increasing or decreasing numerical significance and if a pager notes from the first few bits of an address being received that it follows after its address in the ordered sequence and therefore there is not a call or message for itself, the receiver section of the pager is powered down before the end of the frame in order to save power.
WO 90/06634 discloses the concept of a portable receiver receiving a 32 bit sync code word and checking the sync code word in 2 parts, firstly the first 8 bits and secondly the last 24 bits. If the first part is received having less than two bit errors, the sync code word is considered detected and power control means in the portable receiver powers down the receiving stage for the duration of the second part. If the result is not acceptable, the receiver remains energised for the remaining 24 bits of the sync code word and the result is accepted if there are less than 3 errors in the remaining 24 bits.
This citation also mentions power conservation by disabling the receiving stage or operating a microcomputer in the portable receiver in a low power mode, or by doing both.
Paging systems are structured in that the air interface protocol determines, once the pagers are synchronised, when the receivers should be energised or not. However there are other applications such as telemetry as applied to for example automatic meter reading systems where transceivers coupled to metering units are required to transmit parcels of data in response to the receipt of an infrequently given request. In the interests of power saving the transceivers have to be controlled to minimise the energisation of the receivers whilst ensuring that a prompt response can be given to an interrogation signal.